Double DX Hydronic System

ABSTRACT

A double DX hydronic heating/cooling system includes a primary DX system for maintaining a primary interior fluid loop at a desired temperature range. Secondary DX sub-systems are operatively coupled to the primary interior fluid loop and are operable in either a heating mode or a cooling mode to provide independent control of interior air temperature in different spaces. Each sub-system includes a dedicated water pump to minimize power requirements for the system.

FIELD OF THE DISCLOSURE

The present disclosure relates to geothermal direct exchange (“DX”) heating/cooling systems, which are also commonly referred to as “direct exchange” or “direct expansion” heating/cooling systems.

BACKGROUND OF THE DISCLOSURE

Geothermal ground source/water source heat exchange systems typically include closed loops of tubing that are buried in the ground, or submerged in a body of water. Fluid is circulated through the loops of tubing so that the fluid either absorbs heat from or rejects heat into the naturally occurring geothermal mass and/or water surrounding the tubing. The ends of the tubing loop extend to the surface and are fluidly coupled to an interior air heat exchanger. The naturally warmed or cooled fluid is circulated through the interior air heat exchanger to warm or cool an interior space.

Common and older design geothermal water-source heating/cooling systems typically have a pump for circulating a fluid comprised of water, or water with anti-freeze, in plastic (typically polyethylene) underground geothermal tubing so as to transfer geothermal heat to or from the ground in a first heat exchange step. In a second heat exchange step, a refrigerant heat pump system transfers heat to or from the water. Finally, in a third heat exchange step, an interior air handler (comprised of finned tubing and a fan) transfers heat to or from the refrigerant to heat or cool interior air space.

Newer design geothermal DX heat exchange systems have only two heat exchange steps. DX systems typically have refrigerant fluid transport lines placed directly in the sub-surface ground and/or water. The sub-surface refrigerant lines are typically comprised of copper tubing. A refrigerant fluid, such as R-22, or the like, is circulated through the lines to transfer geothermal heat to or from the sub-surface elements in a first heat exchange step. DX systems only require a second heat exchange step to transfer heat to or from the interior air space, typically by means of an interior air handler. Consequently, DX systems use fewer heat exchange steps and do not require power to run a water pump, and therefore are generally more efficient than water-source systems. Further, since copper is a better heat conductor than most plastics, and since the refrigerant fluid circulating within the copper tubing of a DX system generally has a greater temperature differential with the surrounding ground than the water circulated through the plastic tubing of a water-source system, generally, less excavation and drilling is required, thereby decreasing installation costs.

While most in-ground/in-water DX heat exchange designs are feasible, various improvements have been developed to enhance overall system operational efficiencies. Several such design improvements, particularly in direct expansion/direct exchange geothermal heat pump systems, are taught in U.S. Pat. No. 5,623,986 to Wiggs; U.S. Pat. No. 5,816,314 to Wiggs, et al.; U.S. Pat. No. 5,946,928 to Wiggs; and U.S. Pat. No. 6,615,601 B1 to Wiggs, the disclosures of which are incorporated herein by reference. Such disclosures encompass both horizontally and vertically oriented sub-surface heat geothermal heat exchange means.

Conventional DX system typically heat or cool at least one control medium. A control medium could be, for example, water, water and/or antifreeze, a solid (such as concrete), or a vapor (such as air in an interior room). In a conventional DX system design, the control medium is air in an interior space, and the sub-surface geothermal heat exchange tubing provides heat to the interior air by means of an interior air-handler. In a conventional DX system design, the system is used to either heat or cool, but is not designed to simultaneously heat and cool different control media or similar control media located in different interior spaces.

It is advantageous to maintain or increase the operational efficiencies of a DX system. The subject matter disclosed herein primarily relates to various improvements that will maintain or increase system operational efficiencies, as well as provide a Double DX Hydronic System capable of simultaneously heating and cooling separate control media using a primary sub-surface heat exchanger.

Useful design improvements that will maintain or increase system operational efficiencies in a DX system would encompass an optimal temperature range for water supplied to an interior water loop for a DX system simultaneously operating in both the heating and cooling modes. As used herein, maintaining system operational efficiencies means to preventing degradation of operational efficiency over prolonged periods of use.

Consequently, a means to accomplish at least one of the said primary objectives would be preferable. The present disclosure provides a solution to these preferable objectives, as hereinafter more fully described.

SUMMARY OF THE DISCLOSURE

The exemplary DX systems disclosed herein maintain or increase system operational efficiencies, and provide a system capable of simultaneously heating and cooling separate control media, such as at least one of a vapor (air or the like), a solid, and a fluid/water.

A double DX hydronic system is disclosed which may simultaneously heat and cool separate control media (typically air disposed in two or more separate interior spaces) using at least one primary sub-surface heat exchanger. The primary sub-surface heat exchanger maintains a supply fluid at an optimum temperature level, which testing has demonstrated to be between approximately 50 to approximately 65 degrees F., for use as either a heat source or a heat sink for at least two secondary DX sub-systems. Each of the DX sub-systems includes at least one interior heat exchanger (typically a refrigerant to air heat exchanger, which is commonly referred to as an air handler) to heat or cool a control medium (typically air).

While, in the cooling mode, the temperature range of the supply fluid may be approximately 50-65 degrees F., it has further been found that acceptable cooling performance is achieved with a temperature range of approximately 50 to approximately 80 degrees F. It is counter-intuitive and rather surprising that the expanded range (including 66-80 degrees F.) achieves acceptable cooling performance, since one of ordinary skill in the art would normally think colder supply fluid would improve cooling. For the double DX systems disclosed herein, however, sufficient cooling was obtained in the expanded temperature range. It has been found that supply fluid temperature below 50 degrees F. (sometimes even below 52 degrees if the return air in the interior air handler is below 70 degrees F., which is not normally the case), the interior heat exchanger tubing is more susceptible to developing frost, which decreases system operational efficiencies. Conversely, supply fluid temperatures above 80 degrees F. increase the head refrigerant pressures, which increases the power draw of the compressor and decreases system operational efficiencies.

In heating mode, the supply fluid may also be maintained at approximately 50 to approximately 65 degrees F. to achieve acceptable heating performance. Acceptable heating performance is also obtained across an expanded supply fluid temperature range of approximately 38 to approximately 68 degrees F. The expanded temperature range for the heating mode is also counterintuitive and surprising, as one of ordinary skill in the art would expect that warmer supply fluid would be better for heating. Based on testing, however, it has been found that supply fluid temperatures above 68 degrees F. produces excessive refrigerant head pressure, which increases the power draw of the compressor, thereby decreasing system operational efficiencies.

The double DX hydronic system may include a primary geothermal, sub-surface heat exchanger, a primary compressor box, a primary interior heat exchanger (for transferring heat from the refrigerant to a fluid or liquid), and an interior fluid/water loop, together with at least two secondary interior fluid/liquid to refrigerant heat exchangers, at least two secondary DX system compressor boxes, and at least two secondary interior refrigerant to control medium (the control medium is typically air, but could also be a solid, liquid, water, fluid, or the like) heat exchangers, where a 50 degree F. to a 65 degree F. temperature range is provided and maintained for the liquid supplied to and within supply liquid transport tubing traveling from the primary first interior refrigerant to liquid heat exchanger to the at least two secondary interior liquid to refrigerant heat exchangers of such a Double DX Hydronic System, operating in at least one of the heating mode and the cooling mode.

The primary DX system, via an interior refrigerant to fluid/water heat exchanger, would condition the interior fluid/water supply loop, which fluid/water would be contained within a primary interior fluid/liquid supply transport line/tube. The primary interior supply fluid/liquid transport tubing would preferably be distributed, from the primary interior heat exchanger's primary interior fluid/liquid supply transport line/tube, so as to provide/supply the approximate same temperature fluid/liquid to each respective secondary DX system interior heat exchanger.

In a similar fashion, respective return fluid/liquid transport lines/tubing from each respective secondary DX system interior heat exchanger may be provided which would be combined by a return distributor back into a single primary return liquid transport line/tube into the primary DX system's interior fluid/water heat exchanger.

A respectively distributed interior liquid/fluid/water supply line is provided to at least two secondary and DX sub-systems (which use the conditioned fluid/water, provided by the at least one primary DX system with the sub-surface heat exchanger). The distributed interior liquid operates as either a heat source or a heat sink to provide heated or cooled refrigerant to the interior heat exchangers (typically air handlers). Each respective secondary DX system also has a respectively distributed interior liquid/fluid/water return line that returns the fluid/water back into the primary return line portion of the primary interior fluid/water loop, where the fluid/water is again conditioned, as necessary, by the primary DX system with the sub-surface heat exchanger.

For clarification, a water-source geothermal system has a water loop for heat exchange, but the primary geothermal heating/cooling work is performed by means of water circulating within a sub-surface water containment pipe loop, which pipe loop is usually comprised of polyethylene pipe, as is well understood by those skilled in the art. The subject Double DX Hydronic System does not use a plastic pipe circulating water underground to effect primary geothermal heat exchange, but, instead utilizes a DX system to effect primary geothermal heat exchange. The subject double DX system design solely utilizes an interior fluid/water loop to facilitate interior heat exchange via multiple secondary DX systems.

Further, in a water-source geothermal system, the temperature of an interior water loop is typically dictated by the heating/cooling ability of the sub-surface environment, as opposed to being dictated by an entirely separate DX system, as disclosed herein. Here, the temperature of the sub-surface environment can be dramatically and advantageously augmented by using a primary DX system for purposes of heat transfer with a separate interior fluid/water supply loop. For example, while a water-source sub-surface heat exchanger typically operates on only a 10 degree F. to a 15 degree F. temperature differential between the circulating water and the ground, a primary DX system typically operates on a 30 degree F. to a 100 degree F. temperature differential between the circulating refrigerant and the ground.

Additionally, when water-source system geothermally temperature conditioned water is used in an interior heat exchange loop, the water circulated within the interior loop is commonly made as hot as possible for use in the heating mode, and as cold as possible for use in the cooling mode. Such water-source system designs for the temperature within an interior water loop segment are counterproductive in the subject double DX system design.

In the subject double DX system, copper heat exchange tubing, or the like, is used to circulate refrigerant. The primary, sub-surface heat exchanger directly exchanges heat between the refrigerant and the surrounding sub-surface environment. The geothermally conditioned refrigerant is then used to either heat or cool a fluid (such as water, a mixture of water and anti-freeze, or other fluid) circulating within an interior fluid loop. The interior fluid loop transfers the original geothermal heat gain or loss to at least two secondary DX sub-systems. Here, the secondary DX sub-systems either take heat from, or reject heat into, the interior fluid loop that is primarily conditioned by the primary DX system.

Thereafter, each of the respective secondary DX sub-systems may take heat from or reject heat into the interior fluid loop, thereby to heat or cool refrigerant used in the sub-systems. The heated or cooled refrigerant, in turn, is fluidly communicated to respective interior air handlers to ultimately provide heated or cooled interior air or other control medium. The DX sub-systems may both heat interior air, both cool interior air, or one may heat air while the other cools air, simultaneously. The DX sub-systems may heat or cool control media other than interior air, such as water or solids.

Accordingly, the DX system may provide room-by-room control of air temperature, in which one of the secondary compressor boxes may operate in the heating mode (i.e., furnishing heated air to one room) while the other secondary compressor box simultaneously operates in the cooling mode (i.e., furnishing cooled air to another room). Expanding on the basic two DX sub-system, a secondary DX sub-system may be installed in each room of a building to allow independent temperature control of each room. For example, a first secondary DX sub-system may reject heat into the interior fluid loop from a computer room, kitchen, or the like, while a second secondary DX sub-system pulls heat out of the interior fluid loop to operate in the heating mode to warm a different room. Still further, there may be periods where the primary geothermal DX system is not required to operate at all, thereby providing extremely high overall operational efficiencies.

Finally, a respective liquid circulator pump may be positioned within each respective secondary fluid line servicing each respective secondary DX sub-system interior heat exchanger. The pump may operate only when the secondary respective DX compressor box was on, thereby further maximizing overall system operational efficiencies. By providing smaller pumps dedicated to each secondary DX sub-system, the use of a single, larger, more power consuming, water pump is avoided, and the pumps may operate only when fluid circulation is required in the associated sub-system. Consequently, power consumption required to operate the system is minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed methods and apparatus, reference should be made to the embodiments illustrated in greater detail on the accompanying drawing, wherein;

FIG. 1 is a schematic illustration of a double DX hydronic system constructed according to the teachings of the present disclosure.

It should be understood that the drawings are not necessarily to scale and the disclosed embodiments are sometimes illustrated diagrammatically in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatus, or which render other details difficult to perceive, may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein.

DETAILED DESCRIPTION

The following detailed description is of the best presently contemplated mode of carrying out the subject matter disclosed herein. The description is not intended in a limiting sense, and is made solely for the purpose of illustrating the general principles of this subject matter. The various features and advantages of the present disclosure may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings.

FIG. 1 shows a double DX hydronic system 30 capable of simultaneously heating and cooling separate control media, such as interior air (not shown). The system 30 may generally include a primary DX sub-system 32 and at least two secondary DX sub-systems 34, with unique additional features, as more fully described herein.

The primary DX sub-system 32 may include a primary heat exchanger 1 located below a surface 5 of the ground or water. Accordingly, the primary heat exchanger is alternatively referred to herein as a sub-surface or geothermal heat exchanger. The primary heat exchanger 1 is operably connected to a primary compressor box 2, which in turn is operably connected to a primary first interior heat exchanger 3. The primary heat exchanger 1 may be constructed according to any of the known sub-surface or heat exchanger designs, as are well understood by those skilled in the art. In the illustrated embodiment, the primary heat exchanger 1 has a larger vapor transport tube 4 and a smaller liquid transport tube 6. The vapor and liquid tubes 4, 6 have connection extends disposed above the surface 5 and portions extending below the surface 5 to form the geothermal heat exchanger 1. The connection ends are operatively coupled to the primary compressor box 2.

The primary compressor box 2 may contain a compressor and other components typically provided in a DX system, as are generally understood by those skilled in the art. Accordingly, the compressor box may house a compressor, a reversing valve, an accumulator, an oil separator, and other equipment.

A first interior heat exchanger 3 is provided for transferring heat between the primary heat exchanger 1 and an interior fluid loop. Accordingly, the primary vapor transport tube 4 and the primary liquid transport tube 6 are operatively coupled to the first interior heat exchanger 3. In the illustrated embodiment, the first interior heat exchanger 3 may be a refrigerant to liquid heat exchanger. The liquid side of the heat exchanger may circulate water, a mix of water and anti-freeze, or the like. Any type of known refrigerant to liquid heat exchanger may be used. For example, the first interior heat exchanger 3 may include refrigerant transport tubing coiled around, or disposed within, a second larger fluid transport loop.

The interior fluid loop may include at least a primary supply line 8 and a primary return line 9. A supply distributor 17 may be attached to the primary supply tubing 8 for communicating the primary supply line 8 to multiple distributed supply lines 19 leading to respective secondary DX sub-systems 34. Similarly multiple distributed return lines 20 leading from respective secondary DX sub-systems 34 may be attached to a return distributor 18 for communicating the distributed return lines 20 to the primary return line 9.

The primary supply and return lines 8, 9 are operatively coupled to the secondary DX sub-systems 34 by first and second transfer heat exchangers 11A, 11B. In the illustrated embodiment, the first and second transfer heat exchangers 11A, 11B may be fluid-to-refrigerant heat exchangers for transferring heat from or into the fluid circulated through the primary supply and return lines 8, 9.

The transfer heat exchangers 11A and 11B may be operably connected, via respective secondary vapor lines 12A and 12B and respective secondary liquid lines 13A and 13B, to respective secondary compressor boxes 14A and 14B. The secondary compressor boxes 14A and 14B are, in turn, operably connected to secondary interior heat exchangers 15A, 15B by the secondary vapor lines 12A and 12B and the secondary liquid lines 13A and 13B. The secondary interior heat exchangers 15A and 15B may be interior air handlers. While the interior air handlers 15A and 15B are illustrated in detail herein, they are generally known to include finned tubing, within a box, and a fan that blows interior air over the finned tubing so as to heat or cool the interior air, as is well understood by those skilled in the art. Waved arrows 16 are provided in FIG. 1 to illustrate interior airflow through the secondary interior heat exchangers 15A and 15B.

The respective second interior heat exchangers 15A and 15B could also be comprised of water tubing (not shown herein) that is attached to flooring, or the like, as is well understood by those skilled in the art, for hydronic heating, or the like, as would be well understood by those skilled in the art.

Fluid may be circulated through the first interior heat exchanger 3 using one or more pumps 7A, 7B. In the illustrated embodiment, a pump is disposed in each distributed return line 20, so that the exemplary embodiment includes a total of two pumps. Accordingly, fluid may circulate from the primary supply line 8, through the distributor 17 to the secondary distributed supply tubing 19, through a respective transfer heat exchanger 11A/11B, through the distributed return tubing 20, through the return distributor 18, and through the return tubing 9. Finally, the fluid is circulated through the primary return liquid transport tube 9 back into the first primary interior heat exchanger 3, where the process is repeated as needed to satisfy indoor heating/cooling requirements. The directional flow of the fluid is illustrated herein by arrows 10.

While it may be possible to use one large fluid circulator pump, it is preferable to use multiple smaller liquid pumps for each sub-system 34. In the illustrated embodiment, each pump 7A and 7B is disposed in a respective distributed return line 20. Alternatively, each pump 7A, 7B may be disposed in a respective distributed supply line 19. The use of multiple smaller pumps conserves power in many situations, such as when only one of the sub-systems 34 is operative (in either the heating or cooling mode).

The at least two liquid pumps 7A and 7B are preferably situated within the distributed return lines 20 so as to pull temperature conditioned fluid (not shown) in from the primary supply line 8 exiting the first interior heat exchanger 3. Otherwise, if only a single and larger liquid pump (not shown herein) was placed within the primary supply line 8, or within the primary return line 9, unnecessary liquid/water flow and operational pump power could be wasted via some of the liquid/water traveling through the other distributed liquid to refrigerant heat exchanger, 11A or 11B, that was not required for heating or cooling operation at the time.

The temperature conditioned liquid/water, exiting the first interior heat exchanger 3, travels through the primary supply line 8, and is next shown as being distributed, by means of a first distributor 17, into distributed and smaller supply liquid transport tubing 19, where the temperature conditioned liquid/water next travels to each respective liquid to refrigerant heat exchanger 11A and 11B, so that each respective refrigerant heat exchanger 11A and 11B receives a liquid/water supply which has about the same incoming conditioned temperature, within the preferred temperature range (optimally between fifty and sixty-five degrees F.). In like manner, the distributed return liquid transport tubing 20 is shown as being joined back together by means of a second distributor 18, where the fluid returning with waste temperature fluid is sent into the primary return line 9 for return back into the first interior heat exchanger 3 for temperature re-conditioning, as necessary, by means of the primary compressor box 2 and the primary heat exchanger 1.

The above described design enables one to simultaneously heat and cool control media. In the illustrated embodiment, the control media is interior air. Here one of the respective secondary smaller DX systems and compressor boxes, 14A for example, may furnish cooled refrigerant to its respective second interior heat exchanger/air handler 15A, so as to provide cooled air out of its interior air handler/second interior heat exchanger 15A, while the other respective secondary smaller DX compressor box 14B may be utilized to simultaneously furnish heated refrigerant to its respective second interior heat exchanger/air handler 15B, so as to provide heated air out of its interior air handler/second interior heat exchanger 15B, or vice versa.

While only two respective secondary liquid to refrigerant heat exchangers 11A and 11B, only two secondary smaller DX compressor boxes 14A and 14B, and only two secondary interior heat exchangers 15A and 15B are shown herein, it would be obvious that more than two of each respective item could be utilized as warranted by particular circumstances.

Similarly, while only one primary geothermal DX system sub-surface 5 geothermal heat exchanger 1, only one primary DX system compressor box 2, and only one primary first interior heat exchanger 3 are shown herein, more than one of each respective item may also be used as warranted by particular circumstances. For example, at least two of the illustrated primary heat exchangers 1, at least two of the primary compressor boxes 2, and at least two of the primary first interior heat exchangers 3, may be installed and staged so that multiple primary DX systems would engage as necessary to maintain the preferred supply water temperature ranges to the secondary interior heat exchange equipment.

Here, the primary supply line 8 is shown as feeding, via the first supply distributor 17 and the distributed supply line 19, cooled or heated fluid to the respective liquid to refrigerant heat exchangers 11A and 11B, while the second return distributor 18 combines the distributed return liquid transport tubing 20 back into the primary return line 9, which conveys the liquid/water back to the primary first interior heat exchanger 3 for temperature re-conditioning by means of the primary compressor box 2 and the primary heat exchanger 1.

Interestingly, it might be normally assumed that the lower the temperature of the liquid in the primary supply line 8, the greater the operational efficiency in the cooling mode. Similarly, one might normally assume that the higher the temperature of the liquid in the primary supply line 8, the greater the operational efficiency in the heating mode. However, extensive testing has shown that these apparently logical assumptions are incorrect. Testing has shown that there are optimum temperature ranges for each of cooling mode and heating mode system operation, where maximum operational capacities and operational efficiencies are attained, as next described.

Testing has demonstrated that a 50 degree F. to a 65 degree F. temperature range should preferably be provided and maintained for the liquid supplied to the secondary liquid to refrigerant heat exchangers, 11A and 11B in the cooling mode. In the cooling mode, the fluid exiting the last operative interior liquid to refrigerant heat exchanger, 11B as shown herein for an example, may, and usually will, be greater than 65 degrees F. This fluid, carrying waste heat, ultimately travels back to the primary first interior heat exchanger 3, where the fluid is cooled back down to the preferable supply temperature range of between 50 degrees to 65 degrees F.

Testing has also demonstrated that a 50 degree F. to a 65 degree F. temperature range should also be preferably provided and maintained for the liquid supplied to the secondary liquid to refrigerant heat exchangers, 11A and 11B in the heating mode. In the heating mode, the fluid exiting the last operative interior liquid to refrigerant heat exchanger, herein shown as 11B for example, may be, and usually is, less than 50 degrees F. This fluid carrying waste cold water ultimately travels back to the primary first interior heat exchanger 3, where the fluid may be heated back up to a temperature range of 50 degrees F. to 65 degrees F.

Acceptable, although not optimum, extended temperature ranges for the supply liquid/fluid/water in each respective heating mode and cooling mode may be supplied as disclosed and taught hereinabove.

While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the scope of this disclosure and the appended claims. 

1. A direct exchange geothermal heating/cooling system, comprising: a primary heat exchange sub-system including a sub-surface primary heat exchanger, a compressor box operatively coupled to the primary heat exchanger, a primary interior heat exchanger operatively coupled to the primary heat exchanger, and an interior fluid loop operatively coupled to the primary interior heat exchanger; first and second transfer heat exchangers operatively coupled to the interior fluid loop; a first secondary heat exchange sub-system operatively coupled to the first transfer heat exchanger and including a first secondary compressor box and a first secondary interior heat exchanger; and a second secondary heat exchange sub-system operatively coupled to the second transfer heat exchanger and including a second secondary compressor box and a second secondary interior heat exchanger.
 2. The system of claim 1, in which the primary heat exchange sub-system is operated to maintain fluid in the interior fluid loop within a temperature range of approximately 50 degrees F. to approximately 80 degrees F.
 3. The system of claim 2, in which the system is operable in a cooling mode, and in which the temperature range is maintained in the cooling mode.
 4. The system of claim 2 in which the system is operable in a heating mode, and in which the temperature range is maintained in the heating mode.
 5. The system of claim 1, in which the primary heat exchange sub-system is operated to maintain fluid in the interior fluid loop within a temperature range of approximately 50 degrees F. to approximately 65 degrees F.
 6. The system of claim 5, in which the system is operable in a cooling mode, and in which the temperature range is maintained in the cooling mode.
 7. The system of claim 1, in which the primary heat exchange sub-system is operated to maintain fluid in the interior fluid loop within a temperature range of approximately 38 degrees F. to approximately 68 degrees F.
 8. The system of claim 7, in which the system is operable in a heating mode, and in which the temperature range is maintained in the heating mode.
 9. The system of claim 1, in which the interior fluid loop includes: a primary supply line having a first end fluidly communicating with the primary interior heat exchanger and a second end; a first distributed supply line having a first end fluidly communicating with the primary supply line second end and a second end fluidly communicating with the first transfer heat exchanger; a second distributed supply line having a first end fluidly communicating with the primary supply line second end and a second end fluidly communicating with the second transfer heat exchanger; a first distributed return line having a first end fluidly communicating with the first transfer heat exchanger and a second end; a second distributed return line having a first end fluidly communicating with the second transfer heat exchanger and a second end; and a primary return line having a first end fluidly communicating with the first and second distributed return line second ends and a second end fluidly communicating with the primary interior heat exchanger.
 10. The system of claim 9, further comprising a first pump disposed in the first distributed return line and a second pump disposed in the second distributed return line.
 11. The system of claim 10, further comprising a pump controller configured to selectively operate the first pump only when the first secondary heat exchange sub-system is operative and the second pump only when the second secondary heat exchange sub-system is operative. 